In an annual summary of the climate of 2005, the Climate Monitoring Branch of the National Climatic Data Center provides an overview of conditions throughout the US and around the world during the past year. As the scientific community works to better understand our changing climate, continual monitoring provides vital information on climate variability, continuing trends and the incidence of extreme events. Our primary focus is on placing the recent climate record in historical perspective based on more than 125 years of in-situ temperature and precipitation measurements as well as paleoclimate records that extend our understanding of the earth's climate to the more distant past. Included is a discussion of century-scale variability and trends in temperature and precipitation as well as extreme events such as droughts, tornadoes and tropical storms. The increase in global temperatures recorded over the past 100+ years has occurred in all seasons and throughout almost all regions of the world. There is also evidence that a more rapid rise in global temperatures that began in the 1970s is continuing. Evidence of significant trends in extreme events is less clear. For example, while an extended period of enhanced tropical storm activity in the Atlantic basin that began in 1995 continues, no discernable long-term increase in hurricane frequency or severity has been observed. Analyses of tropical storm records in other basins lead to similar conclusions on a global scale.